Method and apparatus for abrading irregular surfaces

ABSTRACT

A system for abrading irregular surfaces includes a bracket that can be attached to a shop aid. The bracket carries two motors to which abrasive pads are attached, and the positions of the motors are controlled to move abrasive elements over the surface to be abraded. The abrasive pads are attached to abrasive-pad backing of different configurations. Disclosed configurations are generally flat, triangular, and U-shaped.

TECHNICAL FIELD

This invention relates to the abrading of irregularly shaped surfaces.

BACKGROUND ART

It is often necessary to abrade surfaces to prepare them for a varietyof uses. The surfaces are typically abraded by attaching an abrasive padto a motor that moves the abrasive pad in a circular or linear motion.One such motor that is commercially available is an orbital motor, whichoscillates the abrasive pad in a circular motion.

When the surface to be abraded is flat or essentially flat in that itsradius of curvature is large, the abrasive pad can also be essentiallyflat. Complications arise, however, when the surface to be treatedincludes such features as stringers, such as a blade or vent thatprotrude from an essentially flat surface for added strength,ventilation, etc. In this situation, a simple flat pad attached to anorbital motor cannot effectively engage the various surfaces of astringer to abrade them properly. It is particularly difficult to abradeirregular surfaces efficiently with known surface-abrading pads that aredirected by known shop aids such as that sold by Temple Allen Industriesof Rockville, Md. under the trademark EMMA.

A particular problem addressed by the present invention is the abradingof an aircraft wing panel that presents essentially flat surfaces butalso includes stringers of varying geometry that run the length of thewing. These features extend outward from flat portions of the wing,which is toward the interior of a completed wing, to present surfacesthat cannot be abraded with known equipment.

SUMMARY OF THE INVENTION

In accordance with the invention a set of abrasive-pad supportscooperate with a shop aid to hold a known abrasive pad to abradeirregular surfaces, such as stringers. An abrasive-pad backing ismounted on an end effector that is attached to a known shop aid thatmoves the end effector along the surface to be abraded. The endeffectors carry one or more motors that move the abrasive pads withrespect to the surfaces to abrade them uniformly as the shop aid movesthe end effector along the surface to be abraded. The motors can beorbital motors that drive an abrasive-pad backing in a circular motion.

In one embodiment an abrasive-pad backing is configured to abrade upperand lower surfaces of a stringer that extends away from a generally flatsurface. The upper and lower web surfaces of the stringer are typicallynot parallel, and each of the upper or lower web surfaces intersects thegenerally flat surface at a respective curved surface of small radius.The abrasive-pad backing in this embodiment can be a triangular prismwhere two faces of the pad backing are angularly oriented to match theangle between the flat portion of the article to be abraded and arespective web face of the stringer. Thus, one of the abrasive-padsupports matches the angular relationship between the flat portion ofthe article and one of the web surfaces and another of the abrasive-padsupports matches the relationship between the flat portion and the otherof the web surfaces of the stringer. An abrasive pad is attached to eachof two backings, and the two abrasive-pad backings are mounted on an endeffector that holds an abrasive pad on each side of the stringer againstthe surfaces to be abraded.

An abrasive pad can be attached to an abrasive-pad backing in a varietyof ways. For example, a known abrasive pad includes one part of ahook-and-loop (e.g., VELCRO®) fastener, and the abrasive-pad support canhave the matching part of such a fastener. Other fastening mechanisms,such as adhesives, snaps, elastic bands, and the like could be used.

In one embodiment, an abrasive pad is applied to one surface of thebacking and folded over the edge of the backing to engage an adjacentside of the backing. It has been found, however, that the abrasive padis often too thick to form an edge of the abrasive pad that is sharpenough to fit into and abrade the concave portion formed at theintersection of the flat main surface with the surface of the flange. Inthat case, the edge of the abrasive-pad backing is provided with a thinridge that extends along the length of the backing to force thefolded-over abrasive pad to form a thinner edge that engages the concaveintersection.

Another feature of the invention is an end effector that is designed tocontrol the position and motion of the abrasive-pad backings to abrade astringer. This end effector includes a bracket to which two motors aremounted for motion toward and away from each other. An abrasive-padbacking is attached to each of the motors, and the mechanism that movesthe motors toward or away from each other is controlled to maintain apredetermined force of the abrasive pads on the two opposed surfaces ofthe stringer.

Other end effectors are configured to control the operation ofabrasive-pad backings used to abrade features having a plurality ofsurfaces that are themselves essentially flat but are oriented withrespect to each other to form a more complex object. For example, suchan object might be a stringer formed by three intersecting surfaces in abox-like configuration, such as a vent. The end effectors in thisembodiment are designed to hold essentially flat abrasive-pad backingsin either a coplanar arrangement or a parallel facing arrangement toabrade selected surfaces. Yet another end effector is designed tocontrol an abrasive-pad support designed to abrade an outer end of thebox-like object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of an end effector in accordance with a firstembodiment of the invention for abrading a Stringer.

FIG. 2a is a side view of the end effector of FIG. 1.

FIG. 2b is a side view of the end effector showing abrasive-pad supportscloser than shown in FIG. 2 a.

FIG. 3 is a perspective of an abrasive-pad backing.

FIG. 4 is a vertical cross-section of abrasive-pad backing of FIG. 3.

FIG. 5 is a perspective of an end effector for holding abrasive-padsupports in a coplanar arrangement on opposite sides of a box-likefeature.

FIG. 6a is a side view of the end effector of FIG. 5.

FIG. 6b is a side view of the end effector of FIG. 5 with the spacing ofthe abrasive-pad supports being less than in FIG. 6 a.

FIG. 7 is a perspective of an end effector for operating twoabrasive-pad supports facing each other.

FIG. 8 is a side view of the embodiment of FIG. 7 for abrading upper andlower surfaces of a box-like feature.

FIGS. 9a and 9b illustrate the embodiment of FIG. 7 with the upper andlower abrasive-pad supports in different positions.

FIG. 10 is a perspective of an end effector holding an abrasive-padsupport designed to abrade an end of a box-like feature.

FIG. 11 is a side view of the embodiment shown in FIG. 10.

FIG. 12 is a perspective of an abrasive-pad backing used with the endeffector of FIG. 10.

FIG. 13 is a side view of the abrasive-pad support of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an end effector 2 is shown positioned toabrade upper and lower web surfaces of a stringer 4. The stringer, forexample, can be a strengthening stringer for an aircraft wing panel 6.The upper web surface 8 of the stringer is not necessarily parallel tothe lower web surface 10, and the edge 12 is in many instances narrowenough that it does not require separate abrading.

The end effector includes a bracket 14 with a connector 16 forconnecting the end effector 2 to a known shop aid (not shown) forcontrolling the motion of the end effector. The end effector 2 includestwo spaced pneumatic orbital motors 18, each of which operates anabrasive-pad backing 20. The upper motor 18 is mounted directly to thebracket 14, while the lower motor 18 is mounted to a movable plate 22that is movably attached to the bracket 14 to provide control of thespacing between the upper and lower abrasive-pad supports 20. Movementof the plate 22 can be provided by pneumatic cylinder 24, which is inturn controlled by an operator or automatically by a central control(not shown). FIGS. 2a and 2b illustrate operation of the pneumaticcylinder 24 to adjust the spacing of the motors.

FIGS. 3 and 4 show an embodiment of the abrasive-pad backing 20 found inthe end effector of FIGS. 1 and 2 with an abrasive pad 30 attached. Thebacking includes a generally triangular prismatic core 26 and outer foamlayers 28 and 36 for supporting the abrasive pad 30. The backing 20 alsoincludes a narrow, flat ridge 32 (see FIG. 4) that is placed at thepeak, or intersection of two surfaces of the backing and extends abovethe two surfaces to engage a central portion of the abrasive pad 30.This provides the abrasive pad 30 with a rounded edge 34 of small radiusof curvature. This small radius has been found to be effective inallowing the abrasive pad to contact the respective radius intersectionsof the upper and lower web surfaces 8, 10 of the stringer 4 with thewing flange 6.

Another end effector in accordance with the invention is shown in FIGS.5 and 6. The end effector 38 is designed to abrade generally flatsurfaces such as surfaces 40 of a flange as shown in FIG. 6a . Endeffector 38 support two motors 18 to which are attached generally flatabrasive-pad backings 42. In this embodiment the backings 42 arenominally coplanar, but could be at a small angle relative to eachother, for abrading generally flat surfaces 40. The end effector in thisembodiment includes a first bracket 44 that has connector 16 forconnecting the end effector 38 to a shop aid (not shown). A secondbracket 46 pivotally attached to the first bracket 44 supports a motormount 48. The motor mount includes one or more mounting shafts 50 thatengage bushings 52 on the motors for allowing motion of the motorstoward or away from each other. A pneumatic cylinder 54 is mountedbetween the motor mount 48 and one of the motors to move that motoralong the mounting shafts toward or away from the other motor, which isfixed in position on the motor mount. Alternatively, the pneumaticcylinder 54 can be mounted between the motors and both motors allowed tomove along the shafts 50. One or more gas springs 56 are arrangedbetween the motors to dampen vibrations. A handle 58 is provided tofacilitate manual movement of the end effector 38.

FIG. 6a illustrates the end effector 38 positioned with respect to abox-like stringer 60 to abrade essentially flat surfaces of a flange 40.Foam bumpers 62 are provided on the pad backings to absorb vibrationsand allow the abrasive pads 30 to abrade the flange 40 very close to theupper and lower surfaces of the stringer 60. The foam bumpers 62 are incontact with the web surfaces. As the width of a stringer web changes,the pneumatic cylinder extends or retracts to accommodate the changingwidth of the stringer.

FIG. 6b illustrates the position of the motors 18 after the lower motorhas been moved close to the upper motor.

FIGS. 7 through 9 show an end effector 64 configured to abrade upper andlower surfaces of a box-like stringer 60. In this embodiment, the motors18 are mounted to a motor mount 66 by a motor mount bracket 67, themount 66 being pivotally attached to the bracket 46 at a bearing 68. Thearrangement of the connector 16, the pivot axis of the bracket 46 withrespect to the bracket 44, and the rotation of the motor mount providethree axes of motion, for this end effector. (The other end effectorsdescribed herein also have three degrees of rotational motion, e.g.,roll, pitch, and yaw.)

The upper motor 18 in the embodiment of FIGS. 7 through 9 is rigidlyattached to the mount 66. Bars 70 are also rigidly attached and extendforwardly from the mount 66. Shafts 72 connect the bars 70 to plates 74.The shafts 72 can move vertically through bushings in plates 74. Thisallows a known portion of the weight of the end effector assembly to besupported by the force of springs 76.

The lower motor 18 is connected to the mount 66 by a shaft 78, whichcarries the motor on a bearing 80. The vertical motion of the lowermotor is controlled by a pneumatic cylinder. The lower motor is alsomounted to horizontal pins 82 for lateral movement with respect to theupper motor. This lateral offset motion is caused by contact of thelower backing with the flange, and the lower motor is urged outward bygas spring 84.

The offset structure described above allows the two backings to adjustautomatically for offsets in the positions of the flanges above andbelow the stringer. In the embodiment illustrated, the lower backing 42is provided with a foam pad 62. The plate 74 is provided with a taperedbumper 86. The plate 74 allows the end effector 64 to index the upperbacking relative to the upper part of the flange, while the lowerbacking is urged against the lower part of the flange. This feature isillustrated in FIG. 9b and provides more complete coverage of the upperand lower surfaces of the stringer.

FIGS. 10-13 show an embodiment configured to abrade the end of abox-like stringer. In this embodiment, a single motor 18 is pivotallymounted to a bracket 88, which is pivotally mounted to bracket 44 atbearings 90. The motor is pivotally mounted to the bracket 88, theconnector 16, bearings 90, and pivot mounting of the motor provide threedegrees of freedom. An abrasive-pad backing 92 is attached to the motorso that it can engage the end of a box-like stringer 60. Theabrasive-pad backing 92 is generally U-shaped to hold an abrasive pad ina similar shape. A flat part 94 of the backing 92 engages a flat part ofthe end of the stringer 60, while a curved portion 96 on each side onthe flat part 94 engages the corners of the end surface of the stringer60.

The backings disclosed herein, such as backing 92, can be made of foamor other resilient materials. Moreover, a backing can be made ofmaterials such as those shown in FIG. 12 at 98, 100.

Modifications will be apparent to those of skill in the art.

We claim:
 1. Apparatus for abrading an irregular surface comprising abracket supporting two spaced motors, an abrasive-pad backing on eachmotor, and means for moving said motors toward and away from each other.2. Apparatus according to claim 1 wherein said spaced motors are orbitalmotors.
 3. Apparatus according to claim 1 further comprising a connectorfor connecting said bracket to a shop aid.
 4. Apparatus according toclaim 3 wherein one of said spaced motors is mounted to said bracket andanother of said two spaced motors is mounted to a movable plate that ismovably attached to said bracket.
 5. Apparatus according to claim 4wherein said means for moving said motors toward an away from each othercomprises a pneumatic cylinder connected to said bracket and to saidmovable plate.
 6. Apparatus according to claim 1 wherein saidabrasive-pad backing is triangular in cross section.
 7. Apparatusaccording to claim 6 wherein said abrasive-pad backing further comprisesa flat ridge between two adjacent generally flat surfaces.
 8. Apparatusaccording to claim 1 wherein each said abrasive-pad is are generallyflat.
 9. Apparatus according to claim 8 wherein said spaced motors aresupported on mounting shafts to allow said spaced motors to move towardand away from each other.
 10. A method for abrading irregular surfacescomprising the use of the apparatus of claim 1 to move abrasive elementsacross said irregular surfaces.
 11. An abrasive-pad backing comprising agenerally flat part between first and second curved parts at respectiveopposed ends of said generally flat part.